Apparatus for driving plasma panels

ABSTRACT

Apparatus for driving a gaseous discharge display panel in order to display information at selected discrete points in the display panel defined by the intersection of corresponding column and row electrodes, including at least one transformer having multiple secondary coils each connected to a respective column electrode, and at least one other transformer having multiple secondary coils each connected to a respective row electrode, a pair of complementary signal sources each connected to a corresponding one of said transformers, means for addressing selected points in the display panel coupled to a primary coil of respective transformers for entering information into the panel, and the signal sources coupling sustaining signals through the respective secondary coils for maintaining the information in the panel, the signal sources and the addressing means being electrically isolated from the panel electrodes.

9 5 Unite States atent [72] Inventor Ray L. Trogdon Urbana, Ill. [21]Appl. No. 765,938 [22] Filed Oct. 8, 1968 [45] Patented Sept. 28, 1971[73] Assignee University of Illinois Foundation Urbana, Ill.

[54] APPARATUS FOR DRIVING PLASMA PANELS 6 Claims, 3 Drawing Figs.

52 vs. C! 340/324 R,

315/169, 340/166, 340/343 [51] Int. Cl G081) 5/36 [50] Field of Search340/324,

[56] References Cited UNITED STATES PATENTS 3,054,929 9/1962 Livingston315/169 3,098,173 7/1963 Livingston.... 315/169 3,343,128 9/1967 Rogers315/169X VOLTAGE SOURCE VOLTAGE SOURCE Primary Egramineh-John W.Caldwell Assistant Examiner-David L. Trafton Anorney- Merriam, Marshal,Shapiro & Klose ABSTRACT: Apparatus for driving a gaseous dischargedisplay panel in order to display information at selected discretepoints in the display panel defined by the intersection of correspondingcolumn and row electrodes, including at least one transformer havingmultiple secondary coils each connected to a respective columnelectrode, and at least one other transformer having multiple secondarycoils each connected to a respective row electrode, a pair ofcomplementary signal sources each connected to a corresponding one ofsaid transformers, means for addressing selected points in the displaypanel coupled to a primary coil of respective transformers for enteringinformation into the panel, and the signal sources coupling sustainingsignals through the respective secondary coils for maintaining theinformation in the panel, the signal sources and the addressing meansbeing electrically isolated from the panel electrodes.

APPARATUS FOR DRIVING PLASMA PANELS his invention relates to displayapparatus, and in particular to apparatus for driving a gaseousdischarge display panel in order to display information at selecteddiscrete points in the display panel.

The subject matter of the present invention is related to apparatusdisclosed in a copending application of Donald L. Bitzer, H. GeneSlottow and R. H. Willson, U.S. Pat. Ser. No. 613,693, now U.S. Pat. No.3,559,190, filed Dec. 22, 1966 and entitled Gaseous Display and MemoryApparatus. In the disclosure of this prior copending application whichis incorporated herein in its entirety, there is described a panelincorporating gaseous discharge cells of a unique pulsing discharge,wherein the presence or absence of suitably formed wall charges in thecells imparts information. Such a gaseous discharge panel has becomeknown in the art as the plasma panel," and when utilized for displaypurposes is commonly referred to as the plasma display panel. Referencemay also be had to the following publications disclosing the type ofplasma panel related to the present invention, such publications beingincorporated herein in their entirety;

l. Bitzer, D. L. and Slottow, H. G. The Plasma Display Panel-A DigitallyAddressable Display with Inherent Memory, Proceedings of the Full JointComputer Conference, San Francisco, Calif., Nov. 1966.

2. Arora, B. M., Bitzer, D. L. Slottow, H. G., and Willson, R.

H., The Plasma Display Panel-A new device for Information Display andStorage, Proceedings of the Eighth National Symposium of the Society forInformation Display, May 1967.

3. Bitzer, D. L. and Slottow, H. G. The Plasma Display PanelA New Devicefor Direct View of Graphics," Conference on Emerging Concepts inComputer Graphics, University of Illinois Nov. 1967, to be published byBenjamin Publishing Company, New York.

4. Bitzer, D. L. and Slottow, H. G., Principles and Applications of thePlasma Display Panel, Proceedings of the OAR Research ApplicationsConference, Ofiice of Aerospace Research, in the Proceedings of the I968Microelectronics Symposium, I.E.E.E., June 1968.

It is to be understood that the terms plasma panel" and plasma displaypanel" as used herein are defined by and characterized by the gaseousdischarge panel described in the previously mentioned copendingapplication and the above listed publications.

This application is concerned with improved apparatus for driving theplasma panels so that particular display points within the panel definedby pairs of intersecting electrodes can be selected in order to enterthe desired information into the panel. The plasma display paneldescribed in the previously mentioned application and publicationsincorporates a gaseous medium, a first set of row electrodes on one sideof the panel, and a second set of column electrodes on the other sidethereof disposed orthogonal to the row electrodes, the cells or displaypoints each being associated with a respective pair of intersecting rowand column electrodes. It being understood that since the principle ofthe plasma panel being understood that since the principle of the plasmapanel as explained in the previously mentioned copending application isthe manipulation of the wall charges to impart information, either oneor both electrodes associated with the cell can be electricallyinsulated from the gaseous medium. In any case, the gaseous mediumassociated with each pair of electrodes can be discharged by coupling adischarging signal of an amplitude greater than the firing voltage tothe electrodes. The wall charges which are thereafter formed in theseselected cells can be maintained by providing a sustaining signal to thecorresponding electrodes, the sustaining signal having an amplitudesufficient to discharge a cell having wall charges, but not one withoutwall charges. Such selection and sustaining operations are fullyexplained in the prior mentioned copending application and in thepublications, reference to which may be had for this purpose.

Therefore, for each line of the plasma display panel, two types ofdriving signals are required, an addressing or selection signal forselecting a particular pair of lines and thus the cell which is to beadjusted in accordance with the information, and a sustaining signalwhich will maintain this information in the selected cells as long asdesired. Since both of these driving signals must be connected to all ofthe panel electrodes, sufficient isolation must be provided between thevoltage generators or driving sources of these signals. Variousisolation elements have been used, such as resistors or capacitors, butin such cases an additional impedance is placed in series with thedriving sources, which places limitations on these addressing andsustaining apparatus. The number of such isolation elements required inconnection with any panel of practical size has also been a seriousconsideration in the art. One alternative which has been suggested is toemploy individual voltage sources for each electrode on the panel, sincethe ideal generator for driving the plasma display panel is a voltagesource. However, such a technique would required an extremely largenumber of very costly apparatus even considering current semiconductortechnology such as proving integrated circuits for such apparatus. Thus,at the present time it has become necessary to employ the previouslydescribed technique of signal mixing" for addressing and sustaining thedisplay panels, and utilizing a number of isolation elements aspreviously described.

Therefore, in accordance with the principles of the present invention,there is provided novel apparatus for driving the plasma display panelwhich uses the signal mixing" technique, but which greatly reduces thenumber of isolation elements commonly required. The apparatus of theinvention utilizes transformers having multiple secondaries for couplingand suitably isolating the driving signal sources to the plasma panel.Assuming ideal transformers, the present invention provides apparatuswhich is equivalent in operation and performance to the desired systemof having individual voltage generators associated with each electrode.The leakage inductance of the transformers presents some impedance tothe panel, however, this impedance value can be kept to a minimum bycareful construction of the transformers. As an example, thetransformers which have been constructed in accordance with the presentinvention employ printed circuit secondary windings which offer gooduniformity at a reasonable cost.

The invention will be better understood from the following detaileddescription thereof taken in conjunction with the accompanying drawingsin which;

FIG. 1 s a schematic diagram illustrating a plasma panel having 64 cellsand associated electrodes, and the driving apparatus in accordance withthe principles of the present invention for selecting and sustainingcells in the panel;

FIG. 2 is a schematic diagram illustrating the sustaining signalwaveforms provided by the apparatus; and

FIG. 3 is an example of apparatus which can be utilized for providingthe sustaining signals shown in FIG. 2.

Referring now to FIG. I, there is indicated the plasma display panel 10of the type which may be constructed in accordance with the disclosureof the previously mentioned Bitzer, Slottow and Willson copendingapplication or the previously listed publications, and having a seriesof eight row electrodes 12 and eight column electrodes 14. The columnand row electrodes intersect to form 64 different cell points 16 on thedisplay panel 10, any intersecting point or cell being selected bycoupling suitable signals to a respective row and column electrode. Theparticular cell will then be discharged and the desired infonnationentered therein.

A series of transformers 18 each having multiple secondaries connectedbetween respective row electrodes 12 or column electrodes 14 and arespective X-voltage source 20 and Y-voltage source 22. As can be seenfrom FIG. 1. the top four row electrodes 12 are each connected torespective secondaries of a first transformer 18a and the bottom fourrow electrodes 12 are connected to respective secondaries of a secondtransformer 18b. The column electrodes 14 are similarly connected torespective secondaries of transformer l8and 18d. In the first columntransformer 18c, the primary coil 24 is connected between +100 volts anda gating transistor 26, which is gated on by a suitable addressingsignal applied to input terminal 28. Another gating transistor 30 isconnected in parallel with the primary coil 24, and through a suitablesignal applied to input terminal 32 during the sustaining operation, theprimary coil 24 is effectively shorted out so as to reflect a very lowimpedance to the secondary coils 34 of the transformers. Similar gatingtransistors 26 and 30 and connections there between, are provided forall of the primary coils 24 of each of the transformers 18, all of theabove-mentioned interconnections being shown only for transformer 18c onF IG. 1 for convenience.

The voltage sources 20 and 22 provide the sustaining signals illustratedin the upper and lower diagrams of FIG. 2, and one example of anapparatus suitable for use as such a voltage source is indicated in FIG.3. The apparatus shown in FIG. 3 represents either or both the voltagesource 20 and 22, and provides a unipolar output signal having any oneof three voltage levels; e.g., 0, 100 or 200 volts. These three levelsof output are selectively provided by the voltage source of FIG. 3 atthe output terminal 40; the output terminal 40 being connected to arespective secondary coil in each of the transformers associated witheither the column or row electrodes.

As can be seen from FIG. 3, if the transistor 42 is gated on from inputterminal 44, the terminal 40 will be conducted through the low impedanceof transistor 42 to ground or a zero reference potential. If noselecting signal is supplied to input terminal 44 or to input terminal46 of transformer 48, the output terminal 40 is connected to +100 voltsthrough a low value resistor 50. Transistor 52 is coupled between a +200voltage source ad the terminal 40, the operation of transistor 52 beingcontrolled by a transformer 54 coupling the output of gating transistor48 with the input to transistor 52. Thus, in response to a suitableselection signal at input terminal 46, transistor 52 is gated on so thatthe +200 voltage source is connected through the low impedance oftransistor 52 to the output terminal 40. It is to be understood, ofcourse that the selection signals coupled to input terminals 44 and 46of the respective voltage source are obtained from the information to bedisplayed on panel 10.

FIGS. 1-3 can be referred to for the following descriptio of theoperation of the apparatus illustrated therein to selectively fire asingle cell in the panel 10 having 64 cells. In FIG. 2 there isindicated in dashed lines the voltage levels of the signals from therespective voltage sources 20 and 22 applied to the transformers 18. Forconvenience, the row electrodes 12 starting from the top row andproceeding towards the bottom row of the panel 10 have been labeled withreference numerals through 7 respectively, so that the top line 0corresponds to the top row electrode. Similarly, the columns 14 havebeen identified as lines 0 through 7 starting from the first column 14at the extreme left of the panel in FIG. I and proceeding to the extremeright-hand column electrode 14. In the operation of the gaseousdischarge cells in display panel 10, it must be noted that in accordancewith the previous description of such pulsing discharge type cells asdescribed in the previously mentioned Bitzer, Slottow, and Willsonapplication, the cells in the plasma panel only fire once if successivesustaining amplitude excitation signals are of the same polarity. Inconnection therewith, it is assumed that the last firing of the cells inpanel 10 occurred with the column electrodes 14 being coupled to alarger driving voltage than the row electrodes 12. Furthermore, it is tobe understood that if a voltage difference of at least 300 volts issupplied across respective row and column electrodes, the associatedcell will discharge and the information will be entered; whereas, if apotential difference of 200 volts is applied between respective row andcolumn electrodes, the associated cell will discharge and theinformation will be entered; whereas, if a potential difference of 200volts is applied between respective row and column electrodes, thecorresponding cells will discharge only if the cells contain a wallcharge and only if the polarity of the previous sustaining signal isopposite to the subsequent sustaining signal. Similarly, if a sustainingamplitude signal with a suitable slope or duration or with othersuitable characteristics is supplied to the row and column electrodes,the cell having wall charges will discharge only once and the wallcharges will be thereafter removed.

In FIG. I, there is indicated on each side of the transformersecondaries of 34 the value of voltage required for selecting thespecific cell associated with row line 2 and the column line 2. This isprovided in the following manner. Note that the voltage sources 20identified as X-0, X-l and X-3 all have the associated transistor 42operated so that the corresponding terminal points 40 are connected toground or zero potential. The voltage source 20 identified as X-2remains in the normal volt output mode at its terminal 40 which iscorrespondingly connected to column lines 2 and 6. Selection of only thecolumn line 2 is provided by suitably operating the gating transistor 26connected to the primary 24 of the multiple secondary transformer 18c.The primary and secondary windings of transformers 18c and 18d connectedto column lines 0-7 are wound such that the voltage applied across theprimary windings adds to the voltage applied across the prima rywindings adds to the voltage in the secondary windings. Therefore, bycoupling a suitable selecting signal or addressing signal to terminal 28of transistor 26, the 100 volts placed across primary 24 is directlycoupled to the associated secondary windings so that column line 2 isconnected to +200 volts whereas column lines 0, 1 and 3 are connected to+100 volts. Note that the primary 24 of transformer 18d has not beenselected, so that the voltages appearing at the voltage source end ofthe secondary windings of transformer 18d are coupled directly to columnlines 4-7.

In a similar manner, the voltage sources 22 identified as Y-0 through Y3are selectively operated to provide the unipolar output signals of theindicated voltage levels at one side of transformers 18a and 18b.However, the primary and secondary windings of transformers 18a and 186are wound in an opposing manner, such that a voltage applied to theprimary winding 24 of these transformers subtracts from the secondaryvoltage. Therefore, by transferring a selection signal to the primarywinding 24 of transformer 18a simultaneously and in a similar manner asthe selection signal is coupled to transformer 180, the row line 2 isconnected to l00 volts from the respective secondary of transformer 18a.Thus, examining FIG. 1, it can be seen that the only lines having a 300volts discharge potential difference between them are row line 2 andcolumn line 2, thus, the cell associated at their intersection point isdischarged and the suitable information has been entered.

During the sustaining operation, the transformers 18 are not driven, sothat they are only required to provide power to charge the line capacityand the conduction current of a single cell during addressing. In thesustaining operation, it is desired to reflect a low impedance acrossthe secondaries of transformers 18 in order to prevent a voltagebuildup. For this reason, a gating transistors 30 has been provided toall of the transformers (only illustrated in connection with transformerin FIG. 1) so as to operate when the sustainer is on" and thereby shortout the associated primary 24. Another alternative would be to provide asecond primary wound in a suitable manner and closely coupled to thefirst primary 24, the second primary being shorted during the sustainingtime so as to reflect a low impedance short across the secondaries ofthe transformers.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom as modification s will be obvious to those skilled in the art.

What is claimed is:

1. In gaseous discharge display panel apparatus, including a gaseousmedium in said panel, and display points defined by intersecting pairedelectrodes, wherein information to be displayed is entered into thepanel at selected display points by coupling to the respectiveintersecting electrodes, (1) an addressing signal sufi'icient todischarge the gaseous medium and enter the display information at theselected display point, and (2) a sustaining signal sufficient tomaintain the information at the display point,

the improvement comprising:

a pair of transformers each having primary and secondary windings andassociated with at least one of said electrodes;

addressing means for supplying said addressing signal to the selecteddisplay point, said addressing means coupled to the primary andsecondary windings of each of the transformers;

said secondary windings of each transforming interconnecting theassociated electrode and the addressing means; and

sustaining means coupled to the secondary windings of each transformerfor supplying said sustaining signal to maintain the information in saidpanel.

2. Display panel apparatus as claimed in claim 1, wherein saidaddressing means comprises a unipolar signal source providing amultilevel signal, including means for selecting the suitable level ofsaid signal for each electrode so as to discharge the gaseous medium atone of said discrete display points.

3. Display panel apparatus as claimed in claim 2, wherein saidaddressing means includes a selection transformer having the secondarywinding associated with the electrode to be addressed for increasing thepotential difference between the addressed electrodes sufficient todischarge the gaseous medium at the associated display point.

4. Display panel apparatus as claimed in claim 3, wherein said selectionmeans includes first drive means coupled to the primary winding of oneof said selected transformers for increasing the voltage level of saidunipolar signal at the output of the associated secondary windings, andsecond drive means coupled to the primary winding of the other of saidselected transformers for decreasing the voltage level of said unipolarsignal at the output of the associated secondary windings.

5. Display panel apparatus as claimed in claim 2, wherein one of saidsignal levels corresponds to said sustaining signal applied to all ofsaid electrodes.

6. Display panel apparatus as claimed in claim 1, including meanscoupled to each primary winding for effectively lowering the impedanceof each secondary winding during the application of said sustainingsignal to the panel electrodes.

22: 8? UNITED STATES PATENT OFFICE CERTIFICATE 'OF CORRECTION Patent No.3,609 ,746 Dated September 28, 1971 Inventor (s) y gdOn It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

' Column 1 line 40 after ""Research' insert -Arlington, Va.

March 1968. Also published-.

Column 1, lines 59, 60 delete "being understood that since the principleof the plasma panel".

Column 2, line 20, "required" should be --require-.

Column 2, line 49', "5" should be -is-.

"Column 3, line 3, "l8and" should be --l8c and-.

Column 3, line 35, "ad should be -and--.

Column 3, line 55, after "electrode" delete and insert --l2 and thebottom line 7 corresponds to the bottom row electrodenm Column 3, line73 et seq., delete "the associated cell will discharge and theinformation will be entered; whereas if a potential difference of 200volts is applied between row and.

Column 4, line 1, delete "column electrodes".

Column 4, line 25, delete "applied across the primary windings adds tothe voltage".

Column 4, line 71, "modification 5" should be --modif'ications.

Column 6, line 4, delete "a" Column 6, line 4, after"'selection"' insert-means couple-d to the primary winding of each selected--.

Signed and sealed this 13th day of June 1972.

SEAL Attestz' EDWARD M.FLETCHER,JR. ROBERT GOTT SCHALK Attestlng OfficerCommissioner of Patents

1. In gaseous discharge display panel apparatus, including a gaseousmedium in said panel, and display points defined by intersecting pairedelectrodes, wherein information to be displayed is entered into thepanel at selected display points by coupling to the respectiveintersecting electrodes, (1) an addressing signal sufficient todischarge the gaseous medium and enter the display information at theselected display point, and (2) a sustaining signal sufficient tomaintain the information at the display point, the improvementcomprising: a pair of transformers each having primary and secondarywindings and associated with at least one of said electrodes; addressingmeans for supplying said addressing signal to the selected displaypoint, said addressing means coupled to the primary and secondarywindings of each of the transformers; said secondary windings of eachtransforming interconnecting the associated electrode and the addressingmeans; and sustaining means coupled to the secondary windings of eachtransformer for supplying said sustaining signal to maintain theinformation in said panel.
 2. Display panel apparatus as claimed inclaim 1, wherein said addressing means comprises a unipolar signalsource providing a multilevel signal, including means for selecting thesuitable level of said signal for each electrode so as to discharge thegaseous medium at one of said discrete display points.
 3. Display panelapparatus as claimed in claim 2, wherein said addressing means includesa selection transformer having the secondary winding associated with theelectrode to be addressed for increasing the potential differencebetween the addressed electrodes sufficient to discharge the gaseousmedium at the associated display point.
 4. Display panel apparatus asclaimed in claim 3, wherein said selection means includes first drivemeans coupled to the primary winding of one of said selectedtransformers for increasing the voltage level of said unipolar signal atthe output of the associated secondary windings, and second drive meanscoupled to the primary winding of the other of said selectedtransformers for decreasing the voltage level of said unipolar signal atthe output of the associated secondary windings.
 5. Display panelapparatus as claimed in claim 2, wherein one of said signal levelscorresponds to said sustaining signal applied to all of said electrodes.6. Display panel apparatus as claimed in claim 1, including meanscoupled to each primary winding for effectively lowering the impedanceof each secondary winding during the application of said sustainingsignal to the panel electrodes.